Focal seizures are created in monkeys, at birth and at pubescence, by injecting 25,000 units of penicillin into the right face-hand area of the cerebral motor cortex. The development and propagation of the seizure is monitored by electroencephalography, electromyography and clinical observations. At selected intervals during the propagation of the focal seizures the animal is decapitated, the head frozen and the active subcortical neuronal aggregates are delineated by an increase in the regional cerebral blood flow as determined by the 14C antipyrine method. The structures so identified are sampled for microassay of neurotransmitters or their enzymes.